Project Summary Smoking is the most important modifiable risk factor for adverse pregnancy outcomes including preterm birth, neonatal death, and maternal complications. Smoking rates in pregnancy remain unacceptably high. Rates of smoking cessation during pregnancy are low, particularly in underserved populations, and currently approved pharmacotherapies for smoking cessation either are considered unsafe in pregnancy or have uncertain effectiveness. Identifying safe and effective interventions, which might mitigate the adverse effects of smoking on maternal-fetal outcomes, is a major public health priority. Our group has found that smokers, both pregnant and non-pregnant, have a relative deficiency in n-3 long-chain polyunsaturated fatty acids (LCPUFAs). We hypothesize that smoking-induced n-3 LCPUFA relative deficiencies may be an important mechanism contributing to tobacco-related adverse pregnancy outcomes and that n-3 LCPUFA supplementation specifically targeted to pregnant smokers may reduce these complications. Support for this hypothesis comes from a recent secondary analysis of the Omega-3 Fatty Acids Supplementation to Prevent Preterm Birth trial that found that only smokers taking n-3 LCPUFAs had a reduction in preterm labor risk as compared to non-smokers. While compelling, this study was a post hoc analysis that included only a small sample of smokers and did not collect data on smoking behaviors during follow up. Yet the ascertainment of longitudinal smoking behavior is critical, as some clinical studies have found that supplemental n-3 LCPUFAs might also reduce nicotine cravings, and lower daily cigarette use. Thus, smokers may doubly benefit from replenishing n- 3 LCPUFAs via lower risk of preterm labor and/or increased smoking cessation. To address these knowledge gaps, we are proposing a multi-center, randomized, placebo-controlled, double-blinded study of n-3 LCPUFA supplementation in 400 pregnant smokers. We will collect detailed information on smoking behavior, validated biological markers of cigarette exposure (urinary cotinine, end-expiratory carbon monoxide) and biomarkers of n-3 LCPUFA status (red blood cell phospholipid membrane fatty acids). Our specific aims of this proposal are to 1) determine the effect of supplemental n-3 LCPUFAs on gestational age at delivery and preterm labor in pregnant smokers and 2) determine the effect of n-3 LCPUFA supplementation on tobacco use in pregnant smokers. Through our recently completed pilot study, we have optimized our recruitment and retention strategies and determined the tolerability of our intervention. Our research team includes experienced researchers with prior successes in recruiting pregnant women for clinical studies and performing interventional studies for smoking cessation. We will recruit potential participants from eight obstetrics clinics across the Middle-Tennessee area. This will be the first study of supplemental n-3 LCPUFAs conducted exclusively in pregnant smokers. Our study could have a major translational impact on both adverse tobacco- related birth outcomes and smoking cessation efforts.